The present invention relates to a rotating drum vacuum filter and a method of filtering material using such a filter. More particularly, the present invention relates to a rotating drum vacuum filter for recovering enzymes from a fermentation broth. The present invention also relates to filtration systems and methods of filtering using such systems.
Rotating drum vacuum filters have been used to separate components from a sample medium. Typically, the rotating drum vacuum filter is rotated such that a portion of the drum passes through a container containing a sample medium. Filtrate filtered through the drum is carried away or collected from an interior of the drum. Other components from the sample medium, for example, larger components that do not pass through the drum, typically remain on a layer of filter medium that has been applied to the outer surface of the drum. As the drum rotates through then out of a sample medium to be filtered, a thin layer of the filter medium along with sample medium that did not pass through the drum is scraped off of the outer surface of the drum with a scraping blade, forming a thinner layer of filter medium. The thinner layer of filter medium on the outer surface then passes through the sample medium to filter more filtrate through the drum. With each revolution of the drum, the scraping blade is moved closer to the drum and the layer of filter medium becomes thinner and thinner. Frequently, the drum must be stopped, the sample medium must be removed, and a new full-thickness layer of filter medium must be applied to the outer surface of the drum.
A need exists for a rotating drum vacuum filter that does not require frequently shutting down the filtering operation to rebuild the layer of filter medium on the outer surface of the drum.
In enzyme recovery processes using rotary drum vacuum filters, process speed has typically been run slowly so as to maximize the amount of enzyme recovered from a fermentation broth. High speed processing results in incomplete recovery and filter medium and sample medium scraped from the drum typically includes a large amount of wasted enzyme. A need further exists for an enzyme recovery process that uses a rotating drum vacuum filter that can run at high speed and efficiently recover more complete amounts of enzyme from a fermentation broth.
The present invention provides a rotating drum pressure differential filter that includes a device for continuously refreshing a layer of filter medium on the outer surface of the drum such that there is no need to shut down the filtering operation to refresh or rebuild the filter medium. The present invention also provides a filtration system that employs at least one rotating drum pressure differential filter according to the present invention and at least one other rotating drum filter. The present invention also provides a method of enzyme recovery wherein a high percentage of recoverable enzyme is recovered from a fermentation broth during a high speed multi-stage process. In addition, the present invention relates to a filter medium application kit adapted to be retrofitted to existing rotating drum vacuum filters.
A rotating drum pressure differential filter according to an embodiment of the present invention includes a drum, a drive to rotate the drum, a source of differential pressure, a container for containing a sample medium, a scraper adapted to be positioned adjacent the drum, and an applicator adapted to be positioned adjacent to the drum for directing a layer of filter medium toward the outer surface of the drum and applying, rebuilding, or refreshing a filter cake on the drum. In a preferred embodiment of the present invention, the drum is rotatable about an axis of rotation. The drum includes at least one sidewall having an inner surface that at least partially defines an inner chamber, and an outer surface to which a layer of filter medium can be applied for forming a filter cake. The sidewall of the drum includes at least one opening for allowing the passage of fluid, such as a filtrate, from outside the drum to the inner chamber. The drive is designed to rotate the drum about the axis of rotation. The source of differential pressure provides a lower pressure in the inner chamber than outside the drum in the vicinity of the drum, for example, outside the drum in the environment immediately adjacent the at least one opening. The container is preferably positioned with respect to the drum such that, in operation, the drum is rotated about the axis of rotation and at least a portion of a layer of filter medium applied to the outside surface of the drum, also referred to as a filter cake, rotates within the container to contact sample medium disposed within the container. In a preferred embodiment of the present invention, the sample medium is an enzyme fermentation broth. The scraper is adapted to scrape a layer of filter medium from the drum as it rotates and the scraper can be provided with means to slightly advance the scraper towards the drum as the drum rotates. In a preferred embodiment, the applicator is a spray nozzle that applies a mixture, preferably a slurry, of diatomaceous earth mixed or suspended in a liquid such as water.
According to a preferred embodiment of the present invention, the rotating drum pressure differential filter includes a means, such as a control unit, to simultaneously operate the scraper and the applicator such that, in operation, the applicator directs a layer of filter medium toward the outer surface of the drum at the same time that the scraper scrapes a layer of filter medium from the drum.
According to embodiments of the present invention, a method of separating components from a sample medium is also provided and comprises rotating a rotating drum pressure differential filter of the present invention through a sample medium and causing a relatively lower pressure inside the drum that forces filtrate through a filter cake and through openings in the wall of the drum. The method further includes scraping at least a portion of the layer of filter medium from the outer surface of the drum after the portion contacts the sample medium, and applying filter medium to the outer surface of the drum after the scraping operation to rebuild or form a fresh layer of filter medium that is subsequently contacted with the sample medium. Preferably, the scraping and applying are performed simultaneously.
In another embodiment of the present invention, a system of two or more rotating drum pressure differential filters is provided wherein at least one of the filters is a filter according to the present invention. The system includes a conveying means or device to convey scraped filter medium and sample medium from at least one of the drums to at least one other rotating drum pressure differential filter whereby recoverable components that were not recovered by the first drum can subsequently be recovered through use of another drum. A two-stage recovery method using the system is also provided according to embodiments of the present invention.
According to yet further embodiments of the present invention, a method of reducing the downtime of a rotating drum pressure differential filter is provided whereby downtime is reduced by employing a rotating drum pressure differential filter according to the present invention and simultaneously applying a fresh layer of filter medium while scraping a used layer of filter medium. The simultaneous scraping and applying obviates downtime associated with traditional methods of filtration whereby no simultaneous rebuilding, refreshing, or reforming of a filter layer is provided and instead the filter needs to be frequently stopped so that a brand new filter cake can be formed.
In yet other embodiments of the present invention, a method of increasing the throughput of an enzyme fermentation recovery process is provided whereby filtered sample medium scraped from a first rotating drum pressure differential filter is conveyed to a second rotating drum pressure differential filter to further separate or recover enzyme from a previously filtered sample medium scraped from a first filter.
In yet another embodiment of the present invention, an applicator device is provided that is adapted to be positioned with respect to an existing rotating drum filter having a scraper. The device includes an applicator for applying a layer of filter medium to the outer surface of the rotating drum filter or to an existing layer of filter medium on the rotating drum filter. The applicator device further includes a positioning structure to position the applicator relative to the scraper such that in operation of the filter, the applicator is maintained at a constant distance from an outer surface of a layer of filter medium disposed on the outer surface of the drum. According to preferred embodiments of the present invention, the applicator includes a nozzle and may further include a pressurized gas conduit, and a pressurized filter medium conduit, whereby the nozzle combines pressurized gas from the gas conduit with pressurized filter medium from the filter medium conduit, to form a spray. Preferably, the pressurized filter medium conduit is disposed within the pressurized gas conduit and at least the filter medium is recirculated through its respective conduit.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.